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(NC)-How well do you know your soil? It's an important question for the health of the plants in and around your house. Good soil does more than provide a foundation for roots to grab on to. Well-structured soil lets the roots breathe easily, provides the right amount of nutrients and water to the plant, and has the right pH balance for the kind of plants you're trying to grow.

Poor soil can inhibit plant growth in a number of ways. If it has too high a clay content, it will compact easily, drain poorly, prevent air from getting to the roots, and dry into hard clumps. If it's too sandy, it will drain too quickly, erode easily and have difficulty holding nutrients for the plants to use. Good soil strikes a balance between these two extremes. When you pick up a handful, it feels moist and loose without falling through your fingers, has a fresh, clean smell, and a rich dark colour.

To find out what your soil structure is like, stir a handful into a clear glass of water and let it sit for several hours, until the water clears. The coarse, heavier sand particles will eventually settle to the bottom, with silt layering the top. The finer clay particles will eventually settle on top, and some humus (organic matter) will likely float on top of the clear water. Looking at the side of the glass, you can tell what your soil is primarily made of.

If it's mostly sand, digging in lots of organic matter such as Hillview Triple Mix will improve it a great deal. If it's mostly silt and clay, it will benefit from the addition of washed sand to help it drain and aerate well.

All soils will benefit from liberal applications of compost. If you don't have your own compost, try Green Earth Premium Compost. Work the soil by turning it over and mixing it well to a depth of at least one foot, before planting.

SOIL pH LEVELS

Acidity or alkalinity in the soil is measured by pH values, on a scale of 1 (most acid) to 14 (most alkaline) with a level of 7 considered "neutral" Each level is ten times more or less than the next, ie. 5 is a ten times more acidic than 6 and 100 x more acidic than 7. A pH level of 8 is ten times more alkaline than 7, and so on.

The pH level influences the availability of nutrients for you plants, and the type of plants you can grow. For example, azaleas and rhododendrons like a lot of iron, a micronutrient that becomes less available to plants as soil alkalinity increases. These plants prefer a more acid soil, where iron is freely available...otherwise, their leaves become yellow between the veins. Unavailability of many other nutrients can have widely ranging, but equally damaging effects.

Most plants will grow well in a pH range of 6.5 to 7.2, where nutrients are readily available to them and this is a good area to strive for. But to start, it helps to know what your present soil pH value is.

You can buy a simple, inexpensive soil test kit from your garden centre, or ask them for local resources for testing soil samples.

Alkaline soils can be neutralized by adding Green Earth Peat Moss, or small amounts of C-I-L' Aluminium Sulphate. Acid soils can be neutralized by adding Green Earth Dolomitic Lime. Be sure to read the label and change the soil pH slowly and carefully, to ensure you don't upset the balance too far in the opposite direction. Compost will also help neutralize soil pH and add nutrients at the same time.

SOIL NUTRIENTS

All plants need a good balance of the major nutrients (Nitrogen, Phosphorus and Potash), as well as minor or "micro" nutrients such as magnesium, copper, iron, calcium, manganese and many others in minute quantities. You can test your soil for the presence of these nutrients, and add those that are needed in the form of fertilizer. They will quickly become available to the plants (providing your soil pH is fairly neutral) and promote healthy growth. Regardless of pH level, the absence of any key nutrient can cause growth problems. Using a good quality general purpose fertilizer like PINK All Purpose Garden Food 8-12-6 will help to ensure plants get the balanced nutrition they need.